1. Field of the Invention
The invention relates to a transistor outline (TO) housing for high frequency applications, and to a method for producing such a housing.
2. Description of Related Art
TO housings for high frequency applications are known.
In particular document DE 102 21 706 B4 describes a TO housing for high frequency applications.
Such a housing comprises a base which is typically formed as a punched metal part.
The base serves to accommodate a chip with photodiode or a laser diode which is used as a transmitter diode or receiver diode in high frequency applications.
Besides the transmitter diode or receiver diode, other electronic components are typically arranged on the TO housing, in particular an amplifier unit.
The chip is connected via signal leads which are passed through the base.
These signal or connection leads are embedded in a sealing compound, usually of glass, whereby they are insulated from the base and mechanically fixed therein.
Moreover, the glass sealing compound hermetically seals the housing.
With the demand for ever increasing transmission performance, the possible bandwidth of a module comprising such a TO housing has to be increased.
Conventional modules comprising a generic TO housing are presently able to transmit data rates of a maximum of 10 Gbit/s.
In future, however, data rates of more than 20 Gbit/s, in particular data rates from 25 to 28 Gbit/s are desirable.
For achieving this, the impedance of signal carrying elements of such a module is crucial, among other things.
The modules used typically exhibit an electrical impedance, simply referred to as impedance in practice, of about 50 Ω.
It will be understood that the impedance is a function of frequency, and that impedance in the context of the invention refers to the impedance in the high frequency range in which the respective devices are typically operated.
In the high frequency range, a change in impedance involves signal loss due to a reflection. It is therefore desirable that the impedance of the signal path of the transmitter or receiver module is matched with the impedance of the module connected therewith.
In particular it is desired that the transmission and reflection losses are kept as low as possible in a range from 0 to 30 GHz.
Problematic in this context are the bonding wires between the connection leads of the TO housing and the chip on which a transmitter or receiver diode is disposed. A long bonding wire will produce an inductance which reduces the bandwidth of the module comprising the TO housing.
Also problematic are the passages sealed with glass. Due to the comparatively high dielectric constant of glass and the relatively narrow passage, a capacitive characteristic will result which also produces signal loss.